Question

I am trying to write a program that will take the users input value and asks whether they want to calculate the value of the numbers 1 to n or the factorial of n!
This is what I have so far

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Project_2_Part_B
{
    class Program
    {
        static void Main(string[] args)
        {
            var Fkeylow = "f";
            var FkeyCap = "F";
            var Skeylow="s";
            var SkeyCap="S";
            int n = 0;
            long factorial = n;

            Console.WriteLine("Input a value n");
            n = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Do you want to calculate factorial or sum");
            Console.WriteLine("Enter F or S");

            var A = Console.ReadLine();

            if (A == Fkeylow)
                Console.WriteLine();

            if (A == FkeyCap)
                Console.WriteLine();

            var B=Console.ReadLine();

            if (B == Skeylow)
                Console.WriteLine();

            if (B == SkeyCap)
                Console.WriteLine();

            Console.WriteLine("Press any key to close...");
            Console.ReadLine();
        }
    }
}

My issue is with the syntax of the calculation to make the code execute the n*(n-1) while n>1.

Answer 1

static void Main(string[] args)
{
    Console.WriteLine("Input a value n");
    string number = Console.ReadLine(); // Read number
    int n = Convert.ToInt32(number); // Converting to int

    Console.WriteLine("Do you want to calculate factorial or sum? ");
    Console.WriteLine("Enter F or S. ");
    string choose = Console.ReadLine(); // F or S

    int result = -1; // To view later

    if (choose == "f" || choose == "F")
    {
        result = 1;
        for (int i = n; i >= 1; i--) // Loop for calculating factorial
            result *= i;
    }
    else if (choose == "s" || choose == "S")
    {
        result = 0;
        for (int i = n; i >= 1; i--) // Loop for calculating sum
            result += i;
    }

    Console.WriteLine(result); // Printing answer

    Console.WriteLine("Press any key to close...");
    Console.ReadLine();
}